The present invention relates to classifying apparatus and methods and, more particularly, to a vibrating screening deck and method of classifying solid particulates.
Vibrating screening decks have been widely used in the past in the classification and separation of particulate solids of varying particle sizes and composition, such as limestone, coal and other ores. Such screening decks have typically comprised a generally rectangular frame which is suspended in operation and which has a screen cloth in the frame upon which the materials to be classified are deposited. The frame and screen in such decks are suspended at an angle and the entire frame with its screen is vibrated to cause the solid particulates to move down the screen. As the materials move down the vibrating screen, solids of smaller mesh size pass through the screen as "unders" and solids of larger dimensions are discharged from the lower end of the screen as "overs".
One of the disadvantages of these prior screening decks and methods is the substantial energy which must be consumed in vibrating the entire deck including its frame. Such decks typically employ a vibrator motor of upwards of 40 horsepower or more. Another disadvantage of such prior decks is that they are susceptible to the need for frequent maintenance in view of the substantial energy which is imparted to the deck over long periods of time. Still another disadvantage of these prior decks is that they are susceptible to blinding of their screens due to the accumulation in the screen mesh of the solids fines.
At least one screening deck has been developed in the past in which an attempt has been made to reduce the substantial energy requirements. In such deck, a plurality of somewhat smaller vibrator motors have been employed which are coupled to a tappet shaft which extends beneath the screen at various locations spaced along the length of the screen. The tappet shaft is coupled by relatively complex linkages to the vibrator motor on the exterior of the frame of the deck and a plurality of tappet arms are positioned on the shaft which move eccentrically to tap the screen from beneath. In such prior screening deck, only the screen is vibrated, rather than the entire frame and, thus, the energy consumption is reduced. However, the particular tappet arrangement in such screening deck necessitates relatively complex linkages and causes localized tapping of the screen both of which result in early wear of the mechanisms and the screen. Moreover, such prior screening deck necessitates fairly frequent adjustment as the screen becomes stretched during use and relies upon the weight of the material on the screen to keep the screen in contact with the tappets. Moreover, such prior screening deck is still subject to substantially the same screen blinding problems as the prior art screening decks previously described.
The classifying apparatus and method of the present invention overcomes many, if not all, of these problems encountered by the prior art. In a classifying apparatus and method incorporating the principles of the present invention, a substantial reduction in power consumption is realized and the apparatus weight is substantially reduced along with the frequency of maintenance. In a classifying apparatus and method incorporating the principles of the present invention, the vibration of each section of the screen may be tailored or fine tuned over the length of the screen in either one or both of frequency and amplitude of the vibration to substantially reduce screen blinding and to realize a substantial improvement in the quality of separation and efficiency of the classification operation. In a classifying apparatus incorporating the principles of the present invention, only the screen is vibrated and this vibration is isolated from the frame and the vibration is directly induced to the screen, eliminating the need for elaborate tappet mechanisms and linkages and resulting in the realization of the aforementioned advantages. In a classifying apparatus and method incorporating the principles of the present invention, tappet assemblies are self-adjusting to the tension on the screen, thereby resulting in uniform pre-loading conditions of the screen against the tappet assemblies, vibration over the width of the screen is uniform, and the vibration occurs at more locations along the length of the screen. Moreover, the tappet assemblies of the classifying apparatus and method of the present invention enhance crowning of the screen and do not substantially rely upon the weight of the material on the screen to maintain the tappets in contact with the screen, thus, resulting in more uniform performance over wide variations in screen loading and materials handled. In a classifying apparatus and method incorporating the principles of the present invention, one or both of the frequency and amplitude of the screen vibration may be varied and fine tuned along the length of the screen as the load on the screen diminishes, thereby substantially further reducing the energy requirements, blinding, and the carryover of overs toward the discharge end of the screen which should otherwise be unders.
In one principal aspect of the present invention, classifying apparatus comprises frame means having a pair of spaced elongate rigid members and screen means in the frame means between members. Beam means extend beneath the screen means and tappet means are fixed to the beam means and contact the screen means. Vibrator means are mounted on the beam means between the frame members so as to directly vibrate the beam means, tappet means and screen means.
In another principal aspect of the present invention, classifying apparatus includes frame means having a pair of spaced elongate rigid members and screen means in the frame means between the members. A plurality of vibration inducing means are spaced along the length of the screen means for vibrating the screen means and control means independently operate respective ones of the vibration inducing means to vary at least one of the frequency or amplitude of the vibrations of the screen means over its length.
In still another principal aspect of the present invention, a method of classifying solids from each other includes the steps of introducing the solids to be classified to an inclined screen, vibrating the screen, and varying at least one of the frequency and amplitude of the screen vibrations between the location at which the solids are introduced to the screen and the opposite end of the screen.
These and other objects, features and advantages of the present invention will be clearly understood through a consideration of the following detailed description.